AVSynthesis: Blending Light and Sound with OpenGL and Csound5

Now we can get started with AVSynthesis. First, edit the data/config.xml file for the runtime options for Csound and OpenGL. I added these options to set up Csound for running with the JACK audio server and to configure OpenGL for my screen dimensions and video frame rate:

<config csound="-+rtaudio=jack -+rtmidi=portmidi 
 ↪--expression-opt -odac:alsa_pcm:playback_ -d -m0 -g -f 
 ↪-M0 -b1024 temp.orc temp.sco" ksmps="16" width="1280" 
 ↪height="1024" fullscreen="false" FPS="30"/>

Other options must be used if Csound is not compiled with JACK or PortMIDI support. See the Csound documentation for information about other startup and runtime options.

Next, I prepared the Csound and Java environments with these commands:

export OPCODEDIR64=/usr/local/lib/csound/plugins64/
export PATH=$PATH:/home/dlphilp/jdk16/:/home/dlphilp/jdk16/bin/

These commands can be added to your home directory's .bashrc file to automate this step.

Next, I used QJackCtl to configure and start the JACK audio server. This step is unnecessary if you're not using JACK, but I advise doing so for best latency.

Finally, I could start the program:

cd $HOME/AVSynthesis
java -Xmx768m -Djava.library.path=./native -cp 
 ↪AVSynthesis.jar:./lib/*  org.hpk.av.AVSynthesis

This command calls Java, sets a memory amount for it, points the Java library path to the AVSynthesis/native directory, declares the classpath (-cp), loads the needed .jar files from the top directory and the lib directory, and launches the application. By the way, the cryptic string at the end is in the AVSynthesis jar file. It's a weird way to start an app, I know, but Java can be like that.

AVSynthesis takes two or more PNG or JPG images, blends them together in an animated sequence and treats that sequence with various transformations made possible by the OpenGL shading language. At the same time, the program creates a soundtrack that follows the same timeline as the video sequence. The soundtrack itself may be heavily treated by the synthesis, processing and composition algorithms provided by Csound. In AVSynthesis-speak, this combination of sound and image is called a layer. By the way, you can add your own PNG and JPG images to the AVSynthesis data/textures directory, and your own soundfiles can be added to the data/loops directory (for processing by the Csound loop instrument generator).

Given the space limitations for this article, it's impossible to describe the variety of controls over the image and sound processors fully. Consider this possible scenario for the audio section alone: up to three sound sources are available per layer, each sound source is one of five generator types, and each generator's sound can be modified further by up to three audio signal processors. Each processor is one of 13 types. Almost every parameter in the synthesizers and the processors can be modulated by one of eight envelope curves, and each curve is also subject to a modification of its time span. As you can see, it's complexity within complexity, and I haven't even considered the possibilities added by the sequencer and the mixer.

Let me describe an uncomplicated project—an exercise to demonstrate AVSynthesis basics. Note that my description only scratches the surface of this program, and that its full power can be seen and heard only in vivo. I've provided links in the Resources section to some demonstration files, but they merely hint at the possibilities. Worse, the necessary video compression codecs are unkind to the vivid clarity of an AVSynthesis real-time performance. With these facts in mind, let's proceed to the project.

AVSynthesis opens to the composition editor, the program's highest level. This screen is similar to a track display in a digital audio multitrack recorder, but a track here performs only one task. Each track is a timeline divided into 30 ten-second sections, and each section contains one stage of a simple three-stage line-segment envelope that controls the visibility and the corresponding audio volume of the track's layer. As we shall see, this envelope itself may be modified by factors working elsewhere within the program.

No text labels or tooltips describe the Composition screen's various functions, so the user must memorize their significance and purposes. Fortunately, there are relatively few functions on this screen. Figure 2 defines the other screen elements, most of which deal with performance controls and save/load functions. Later, we'll consider some of them more closely, but first, let's make a movie, with sound.

Figure 2. The Composition Screen Layout